Chromatin is the physiologically relevant substrate for all genetic processes inside eukaryotic nuclei. The fundamental repeating unit of chromatin is the nucleosome, which consists of 146 base pairs of DNA wrapped around an octamer of core histone proteins. Native chromatin comprises, in addition to nucleosomes, linker histones, such as histone H1, and nonhistone chromosomal proteins, such as the High Mobility Group N (HMGN) proteins. HMGN proteins are abundant nucleosome-binding proteins found in vertebrates, suggested to be involved in the regulation of gene activity. In this Research Proposal, a systematic study of the four known human HMGN proteins is proposed. Specifically, (1) the properties of human HMGN proteins will be analyzed in vivo by studying their interaction with different genes during transcriptional activation; (2) chromatin containing human HMGN proteins will be in vitro assembled and characterized; (3) the biochemical properties of chromatin containing HMGN proteins will be investigated, with special emphasis in their effect on chromatin transcription and remodeling. Together, these studies will contribute to the understanding of the biological functions of the HMGN proteins in the context of chromatin.